There have been various proposals to provide autonomous or robotic machines for performing duties such as cleaning or polishing a floor area, or for mowing grass. In their simplest form, the machine requires a training phase during which the machine is manually led around the area in which it is to work. Following this training phase, the machine will then perform the required work as it follows the path which it stored in its memory during the training phase. Other machines may simply follow a predetermined route which is marked by means such as a cable which is buried beneath the working area. Machines of this type have the disadvantage of requiring supervision or a specially prepared working area.
Other autonomous machines are supplied with a map of the working area, the machine using this map to plan a route around the working area.
There have also been proposals for autonomous machines which are capable of exploring the environment in which they are placed without human supervision, and without advance knowledge (e.g. a map) of the layout of the environment. The machine may explore the environment during a learning phase and will subsequently use this information during a working phase, or the machine may begin working in the area immediately. An autonomous machine shown in WO 00/38025 initially travels around the perimeter of an area, recognises when it has completed a single lap of the area, and then steps inwardly after that and subsequent laps of the room so as to cover the area in a spiral-like pattern. Autonomous machines are also known to build a map of the working area using the information they acquire during the learning phase. Autonomous machines of this type are particularly attractive to users as they can be left to work with minimal human supervision.
Autonomous machines of this kind can cope very well with simple working areas, e.g. rooms with a rectangular shape, but they can often run into difficulties with more realistic working areas, such as those areas with an irregular shape or areas with obstacles placed at various positions within them.
It is also known to provide autonomous machines which derive their power from a mains power supply and which carry a reel of cable which is dispensed as the machine moves around the area. U.S. Pat. No. 4,962,453 shows an example of this kind of machine, which covers a working area by a complex series of fan-shaped coverage patterns.